The invention is directed towards a pseudotetrahedral transition metal complex and the production of xcex1-olefins using the pseudotetrahedral late transition metal catalyst complex.
The chemical industry uses xcex1-olefins as intermediates in a variety of processes. In particular, linear xcex1-olefins are used in the formation of polyolefins such as ethylene butylene copolymers. Other products formed from xcex1-olefins include surfactants, lubricants and plasticizers. Paraffin wax cracking, paraffin dehydrogenation and alcohol dehydration processes can be used to produce xcex1-olefins; however, most of the linear xcex1-olefins currently used in the chemical industry are produced by ethylene oligomerization. Ethylene oligomerization is a desirable route due to the availability and low cost of ethylene. Additionally, the product quality is also acceptable for most applications.
In recent years, the chemical industry has employed the use of organometallic catalysts to produce polymers. While many advances in organometallic catalyst technology have been made, researchers continue to seek superior catalyst compositions. In fact, very recently, novel late transition organometallic catalysts have been discovered which are very effectively used in polymerization processes. More specifically, U.S. Pat. No. 6,037,297 to Stibrany et al., herein incorporated by reference, details group IB (Cu, Ag and Au) containing catalyst compositions that are useful in polymerization processes.
Organometallic catalyst technology is also a viable tool in oligomerization processes which produce linear xcex1-olefins for use as feedstock in various other processes. However, one problem often encountered when using many of these catalyst systems is the propensity to produce xcex1-olefins with very low selectivity (i.e., a Schulz-Flory type distribution with high k values). For instance, many of the linear xcex1-olefins made today utilize a neutral nickel (II) catalyst having a planar geometry and containing bidentate monoanionic ligands. While these planar nickel (II) catalysts do produce linear xcex1-olefins, these catalysis systems exhibit a Schulz-Flory type of distribution over a very wide range (i.e., C4-C30+).
To address the Schulz-Flory distribution problem, chromium metal based catalysts have become popular for use in certain oligomerization processes. More precisely, chromium complexes have been used to oligomerize ethylene in order to form linear xcex1-olefins with improved distributions. In fact, there has been a report of a specific chromium catalyst which selectively trimerizes ethylene to 1-hexene. These techniques employ the use of a chromium compound in conjunction with aluminoxane along with one of a variety of compounds such as nitrites, amines and ethers. Unfortunately, while these techniques have been able to selectively produce xcex1-olefins, polymer is formed as a co-product. Of course, when polymer is co-produced, the yield of desirable product decreases accordingly. Also, as a practical matter, polymer build-up in the reaction vessel can severely hamper production efficiency thereby limiting the commercial use of such processes.
As discussed above, the organometallic catalyst technology now being used to produce xcex1-olefins has two major disadvantages. First, many of the organometallic catalysts produce xcex1-olefins with a Schulz-Flory type distribution. Unfortunately, this Schulz-Flory type distribution is not ideal when short chain xcex1-olefins are desiredxe2x80x94in other words, the selectivity is not good enough to maintain efficient processes. Because xcex1-olefins are used as intermediates for specific products, xcex1-olefins with certain chain lengths are desired. For instance, the following are examples of xcex1-olefin chain lengths that would be desirable as feeds for certain product types: C4 to C8 for comonomer in ethylene polymerization; C10 for lube quality poly-xcex1-olefins; and C12 to C20 for surfactant products. Thus, considerable inefficiency and waste is present when significant amounts of xcex1-olefins are produced having chain lengths outside of the range required for production of a particular chemical. Second, while some of the current organo-metallic catalysts may improve selectivity, most also produce polymer co-product. This lowers the yield of desired product and can also accumulate in the reaction vesselxe2x80x94both of which make commercial use less attractive and inefficient. Hence, there is still a need for improving the selectively and efficiency of linear xcex1-olefin production.
The instant invention provides a metal complex composition and its use in an oligomerization process for producing xcex1-olefins. The metal complex composition comprises the reaction product of a metal compound selected from the group consisting of halides, hydrides, triflates, acetates, borates, C1 through C12 alkyl, C1 through C12 alkoxy, C3 through C12 cycloalkyl, C3 through C12 cycloalkoxy, aryl, thiolates, carbonyl, cyanate, olefins including diolefins and cycloolefins, and any other moiety into which a monomer can insert and mixtures thereof, with an amine ligand wherein said ligand is a nitrogen-containing ligand having one or more nitrogen atoms. Upon recovery, the metal complex has the formula LM(Xxe2x80x2)(X)n, where n equals 0 or 1; X and Xxe2x80x2 are independently selected from the group consisting of halides, hydride, triflate, acetates, borates, C1 through C12 alkyl, C1 through C12 alkoxy, C3 through C12 cycloalkyl, C3 through C12 cycloalkoxy, aryl, tiolates, carbon monoxide, cyanate, olefins, and any other moiety into which a monomer can insert; and wherein L is a nitrogen-containing monodentate, bidentate, tridentate or multidentate ligand with one or more nitrogen atoms and M is selected from the group consisting of Ni, Pd and Pt. The instant metal complex can be used to selectively produce C4 to C12 xcex1-olefins without producing a significant percentage of higher xcex1-Olefins (i.e.,  greater than C12 olefins) or polymer co-product. Thus, the two problems noted above with regard to current oligomerization processes are overcome.
The metal complex can be used directly as the reaction product described above thereby saving process steps and increases the range of possible catalysts which can be used to produce xcex1-olefins and is amenable to high throughput experimentation. Otherwise, the metal complex can be recovered from the reaction mixture and then utilized.
In another embodiment, the invention is a metal complex composition comprising the reaction product of an amine ligand (L) and M-Salt [MX(Xxe2x80x2)n} prepared as described above, and an activating cocatalyst. This embodiment of the invention is particularly useful in oligomerization chemistry.
Also provided for is a method for selectively and efficiently producing C4 to C12 linear xcex1-olefins. The method includes contacting ethylene, an olefinic monomer, under oligomerization conditions with the catalyst composition defined above and an activating co-catalyst.
These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying figure.
In-situ as used herein means that the metal complex is not recovered prior to use, but is, instead, used directly. As used herein, recovered, when referring to the metal complex, means the metal complex crystals or solid are isolated from the solution by e.g., filtration and the recovered solids or crystals have an identifiable structure LM(Xxe2x80x2)(X).